Make it reloadable

The status line isn't cleared away when you C-x 0.
 - CLUE: also happens when the window is very narrow and a large jump
   would clear entire lines, but the lines to be cleared span the
   entire window. For example, M-> in xterm_controls.txt when the
   window is ~20 chars wide.

Preserve column on up/down better.

Need line wrap of some kind.

Catch and handle SIGWINCH.
See http://man7.org/tlpi/code/online/dist/tty/demo_SIGWINCH.c.html